The present invention generally relates to helical scan type magnetic recording and reproducing apparatuses for forming tracks which are mutually separated in a width direction of a tape and, more particularly, to a magnetic recording and reproducing apparatus which records three kinds of signals constituting a color video signal on a plurality of tracks which are mutually separated in the tape width direction by use of a plurality of rotary heads which simultaneously and independently form the plurality of tracks for, at the time of reproduction, a picture a satisfactory quality and having only an extremely small time base deviation.
A helical scan type magnetic recording and reproducing apparatus (VTR) which uses a magntetic tape having a width of 1/2 inch is presently used in various fields. However, in the VTR for home use, the frequency band in which the recording and reproduction can be performed is relatively narrow. For this reason, in the VTR for home use, a luminance signal separated from a color video signal is frequency modulated, a carrier chrominance signal separated from the color video signal is frequency-converted into a low frequency range, and the frequency modulated luminance signal and the frequency converted carrier chrominance signal are frequency-division-multiplexed for recording on and reproduction from the tape. In the present specification, such a recording and reproducing system in which the carrier chrominance signal is frequency-converted into the low frequency range will be referred to as a low-band conversion system. Further, in the VTR for home use, the tape utilization efficiency is improved by employing a system which does not form guard bands at the time of the recording and uses rotary heads having gaps of mutually different azimuth angles to record two mutually adjacent tracks.
On the other hand, in the VTR for business use such as broadcasting and especially in the case of a one-body type VTR having a camera unitarily built therein, there are damands to downsize the apparatus, reduce the weight of the apparatus and obtain a reproduced color video signal having a high picture quality. Hence, the luminance signal and color difference signals are recorded on independent tracks on the tape which has a width identical to that used in the VTR for home use by rotary heads so that a guard band is formed between two mutually adjacent tracks. In the present specification, such a recording and reproducing system will be referred to as a Y/C separation system.
In a VTR employing the Y/C separation system, during a time period in which one rotary head records one field of the luminance signal on one track, another rotary head records one field of the color difference signals on another track. Thus, two tracks are simultaneously formed in each time period of one field. The track recorded with the liminance signal and the track recorded with the color difference signals are formed adjacent to each other along a longitudinal direction of the tape.
The luminance signal and the color difference signals are recorded on and reproduced from independent tracks on the tape according to the Y/C separation system. For this reason, although a moire occurs with a VTR employing the low-band conversion system when the frequency modulated luminance signal and the frequency converted carrier chrominance signal are simultaneously recorded on the same track on the tape which is a non-linear transmission system, such a moire will not occur with a VTR employing the Y/C separation system. In addition, it is possible to reserve sufficiently wide frequency bands for recording and reproducing the luminance signal and the color difference signals. Further, because the VTR employing the Y/C separation system does not record the frequency converted carrier chrominance signal by using the frequency modulated luminance signal as a bias signal, it is possible to improve the signal-to-noise (S/N) ratio of the reproduced color difference signals. As a result, it is possible to obtain a reproduced color video signal having a high picture quality compared to the VTR employing the low-band conversion system.
However, the tape utilization efficiency is poor with to the Y/C separation system because of the need to provide the guard band. Moreover, if the rotary head crosses a guard band during reproduction and scans a track which is adjacent to the track which was to be scanned, the rotary head, which should have produced the luminance signal (or the color difference signal) will reproduce the color difference signals (or the luminance signal) since two mutually adjacent tracks are independently recorded with the luminance signal and the color difference signals. There is no field correlation between the reproduced signals from the two mutually adjacent tracks, and thus, it is also impossible to eliminate crosstalk by a crosstalk cancelling method which uses the field correlation as is done in the VTR for home use which employs the low-band conversion system. Hence, the VTR employing the Y/C separation system has a problem in that the crosstalk is conspicuous in the reproduced picture.
The conventional VTR employing the Y/C separation system simultaneously records and reproduces the luminance signal and the color difference signals on and from independent tracks on the tape by a pair of rotary heads having gaps of mutually different azimuth angles. For this reason, when a tracking error occurs during reproduction, there is a problem in that a time difference occurs between the luminance signal and color reproduced signals by the pair of rotary heads.
Accordingly, in order to eliminate the problems described above, recording the reproducing apparatuses were previously proposed in a Japanese Utility Model Application No. 57-66496 (Japanese Laid-Open Utility Model Application No. 58-170012), Japanese Patent Application Nos. 60-35827 and 60-35828 in which the applicant is the same as the assignee of the preset application. According to the previously proposed apparatuses, three kinds of signals constituting the color video signal are recorded on and reproduced from a plurality of tracks formed in recording regions of the tape which are separated from each other in the tape width direction. Since the recording regions in which the plurality of tracks are simultaneously and independently formed on the tape are completely separated from each other, it is possible to prevent mutual interference among the signals reproduced from the tracks in the different recording regions and hence eliminate the problems of the conventional apparatus.
However, in the previously proposed apparatuses, there is a question as to which tracks the three kinds of signals constituting the color video signal, that is, the luminance signal and two kinds of color difference signals, for example, should be recorded on. The signals reproduced from the tracks in the recording regions which are separated from each other in the tape width direction include time base deviations (jitters) which are mutually different. Generally, the tape is moved in a state where the lower part of the tape is stably guided by a tape guide. Accordingly, there is less jitter in the signals reproduced from the tracks in the lower part of the tape compared to the signals reproduced from the tracks in the upper part of the tape.
The tape is wrapped around the outer peripheral surfaces of an upper rotary drum and a lower stationary drum with the lower part of the tape guided by a tape guide formed on the lower stationary drum. For example, a pair of rotary heads which are mounted on the upper rotary drum at positions separated from each other in the axial direction of the upper rotary drum simultaneously form two independent tracks which are mutually separated in the tape width direction. In this case, in a vicinity of an entrance position of the upper rotary drum where the pair of rotary heads start to make sliding contact with the tape, it is known that the thickness of an air film which is formed between the tape and the outer peripehral surface of the upper rotary drum is larger toward the upper part of the tape and is largest at the upper edge of the tape. For this reason, the contact pressure with which the rotary head makes contact with the tape and the S/N ratio of the signal which is recorded and reproduced are poor in the tracks which are located close to the upper edge of the tape.
On the other hand, when the luminance signal and the two kinds of color difference signals are compared, the frequency band of the luminance signal is wider than those of the color difference signals. Further, high frequency components (information related to a small area in the picture) of the color difference signals are not transmitted as much as a high frequency component of the luminance signal. For this reason, even when there is slight jitter in the color difference signals, the effects of such slight jitter in the color difference signals are visually inconspicuous compared to a jitter in the luminance signal. In addition, the luminance signal includes synchronizing signals which are used in a servo system and a monitor, and this also makes desirable for the luminance signal to be free of jitter.
Moreover, in the previously proposed apparatuses, the signals simultaneously reproduced from the independent tracks in the recording regions which are separated from each other in the tape width direction include jitters which are mutually different due to inconsistency in the tension of the tape, the stretch of the tape and the like. As a result, it is extremely difficult to make the time bases of each of the reproduced signals perfectly coincide with each other.